[MUSIC] Hi, everyone, we will talk about how MR image is formed in this week. The content is how to sequence gradient pulses to get an image, and also we'll talk about slice selection, and K-space, and frequency encoding, and phase encoding. This is going to be probably one of the most difficult part for you to understand for the MR imaging. Okay, but let's try. Okay, how to sequence gradient pulses to get an image. So, let's review the previous concept of free induction decay. So, when a subject is placed inside a strong magnetic field. A spin is going to rotate and there will be spin excess which generates MR signal. So when other pulses is applied, the sum of the spins parallel to the field move to anti-parallel to the field. So the longitudinal component decreased but the transpose component start to appear. And then when other pulses is stopped, and then the transpose component can be detected in the RF coils, which is going to be used for MR imaging. And that transverse component is called free induction decay. And eventually, the magnetization is going to come back to original. So longitudinal component will be returned back to original. And transverse component decays back to zero. So during this period, we can observe a signal, called free induction decay. Okay, that's what we talked in the previous week. So, this is MR signal, magnetic resonance and data location. And then how can we acquire data to generate MR imaging, and that is the concept that we consider here. So this magnetic resonance, and data location should be combined with gradient pulses to form an imaging. So, for the MR imaging, so this FID signal cannot be directly used and then converted to MR imaging. And the reason is there is not enough time for spacial encoding. And then, how can we sequence gradient pulses relative to RF pulse and ADC sampling? So this ADC and RX is all about the data location. Okay, we will talk about, we'll use these terms in an interchangeable way. And also transmission, TX represents transmission. In which it is almost the same as magnetic resonance or RF pulse, or those two terms may be also used in a similar way. Okay, and then how can we sequence gradient pulses relative to this RF pulse and ADC data location to form an MR image? Okay, that is going to be the contents we'll talk in this week. So here are the gradient pulses. And then, so gradient pulses spatially modulate the magnetic field strength, and that is proportional to the procession frequency. That is what we discussed in the previous weeks. And to get a topographic MR image, so gradient pulses along X and Y, and Z, should be combined with RF pulse and ADC data location, RX in a special way. Okay, as shown here, this is overview of this concept. Okay, along the Z direction, for instance, we can excite, we can cause magnetic resonance only in the slice of interest, and that is going to be excited. And then the excited two dimensional plane will be encoded along X and Y direction, which is called frequency encoding and the phase encoding. And then Fourier transform, applying for Fourier transform to this acquired data, which is called K-space, and that is going to be converted to MR image. Okay, this is our concept that we will discuss in day three.
